The work presents the characterization by dynamic thermal methods of some bisazopolyethers with flexible spacer. A MOM-Budapest derivatograph was used for the thermal analysis that enables the simultaneous registration of the thermogravimetric curve (TG), of the derivative thermogravimetric curve (DTG) and of the differential thermal analysis (DTA). The registrations were made in air - static conditions, at different heating rates ( 5, 10, 15, 20K/min) by keeping constant the other operational parameters in order to obtain comparable data. The study led to some conclusions about the structure -thermostability - degradation mechanism. The thermostability is determined by the presence of the azo groups, but it may be modified, depending on the nature and the relevance of the co-monomer. The mechanism of the thermal degradation is complex, by successive reactions, the fragmentation of the chain being influenced by the chemical structure and the heating rate.